Electron transfer kinetics with both reactant and product attached to the electrode surface

An open circuit charge injection (“coulostatic”) technique was employed to measure electron transfer kinetics for reactants confined to the surface of graphite electrodes. Iron protoporphyrin IX exhibited kinetics that were too fast to measure but the rate constant for the reduction of 9,10-phenanthrenequinone at its formal potential in 1 M HClO₄ was evaluated as 320 s^?1 at 22°C. Measurements of the rate constant at temperatures between 5 and 50°C produced a linear Arrhenius plot with an intercept which was rationalizable in terms of a frequency factor near kT/h. This result is utilized in a discussion of the factors that control the electrochemical reactivity of reactants in attached and unattached states.